The present disclosure relates generally to a method and a device for infusion of fluids.
Diabetes mellitus is a disease of major global importance, increasing in frequency at almost epidemic rates such that the worldwide prevalence in 2006 is approximately 170 million people and is predicted to at least double over the next 10-15 years. Diabetes is characterized by a chronically raised blood glucose concentration (hyperglycemia) due to a relative or absolute lack of the pancreatic hormone insulin. Within the healthy pancreas, beta cells, located in the islets of Langerhans, continually produce and secrete insulin according to the blood glucose levels, maintaining a near constant glucose levels in the body.
Much of the burden of the disease to the patient and to health-care resources is due to the long-term tissue complications, which affect both the small blood vessels (microangiopathy, causing eye, kidney and nerve damage) and large blood vessels (causing accelerated atherosclerosis, with increased rates of coronary heart disease, peripheral vascular disease and stroke).
The Diabetes Control and Complications Trial (DCCT) demonstrated that development and progression of the chronic complications of diabetes are greatly related to the degree of altered glycemia as quantified by determinations of glycohemoglobin (HbA1c). (See, for example, DCCT Trial, N Engl J Med 1993; 329: 977-986, UKPDS Trial, Lancet 1998; 352: 837-853. BMJ 1998; 317, (7160): 703-13 and the EDIC Trial, N Engl J Med 2005; 353, (25): 2643-53.) Thus, it is important to maintain euglycemia by performing frequent glucose measurements and by making adjustments of insulin delivery accordingly.
Insulin pumps can be used for measurement and adjustment of insulin delivery. Some insulin pumps deliver rapid acting insulin 24 hours a day through a catheter placed under the skin. The total daily insulin dose can be divided into basal and bolus doses. Basal insulin can be delivered continuously and/or periodically over a 24-hour period to keep the blood glucose levels in range between meals and overnight. Diurnal basal rates can be pre-programmed or manually changed according to various daily activities. Insulin boluses can be delivered before meals or during episodes of high blood sugar levels to counteract carbohydrates loads.
Insulin pumps can compute a bolus dose using several parameters. For example, insulin pumps can use any of the following parameters:                Amount of carbohydrates (Carbs) to be consumed, alternatively defined as “servings”, where one (1) serving equal approximately 15 grams of Carbs;        Carbohydrate-to-Insulin ratio (CIR), i.e., the amount of carbohydrates balanced by one unit of insulin;        Insulin sensitivity (IS), i.e., the amount of blood glucose value lowered by one unit of insulin;        Current blood glucose level (CBG);        Target blood glucose level (TBG), i.e., the desired blood glucose level. TBG for most people suffering from diabetes is in the range of 90-130 mg/dL.        Residual insulin (RI), i.e., the amount of stored insulin remaining in the body after recent delivery of still active boluses. This parameter is relevant when there is a short time interval between consecutive boluses (e.g., less than 5 hours).        
In U.S. Pat. No. 6,936,029, a pump provided with a bolus calculator and a procedure to calculate the amount of insulin to be administered is described. The procedure is based on the following formula for calculating a bolus:
where TC is the total amount of carbohydrates, CIR is the carbohydrate-to-insulin ratio, TBG is the target blood glucose, CBG is the current blood glucose, IS is the insulin sensitivity and RI is the remaining insulin (i.e., “residual insulin”).
The insulin sensitivity (IS) may be determined, for example, according to the “2200 to 1600 rules” commonly used by type 1 diabetes patients using rapid acting insulin (e.g., Humalog®, Novolog®). Specifically, the user's IS can be determined by dividing the value corresponding to an appropriate Rule (i.e., a standard value, such as 1800, which is divided by a daily insulin dose to compute an estimated insulin sensitivity for the patient) by the total daily dose of rapid-acting insulin (e.g., if the total daily insulin dose is 40 units and the 1800 rule is used, the insulin sensitivity factor would be 1800 divided by 40=45 mg/dl/unit). For example, the table of FIG. 1 shows the point drop per unit of insulin (insulin sensitivity) corresponding to various rules (adapted from Using Insulin© 2003)
The carbohydrate to insulin ratio (CIR) may be determined, for example, according to the “450 to 500 rules” commonly used by type 1 diabetes patients using rapid acting insulin (e.g. Humalog®, Novolog®). The user's CIR can be determined by dividing the value corresponding to an appropriate Rule by the total daily dose of rapid-acting insulin (e.g., if the total daily insulin dose is 40 units and the 450 Rule is used, the carbohydrate to insulin ratio (CIR) would be 450 divided by 40=11 gram). The table in FIG. 2 shows carbs (in grams) covered by 1 unit of insulin (CIR ratio) according to the various Rules (adapted from Using Insulin© 2003).
The residual insulin can be determined according to the pharmacokinetics of rapid acting insulin (e.g., Humalog®, Novolog®). The table in FIG. 3 provides the units of residual insulin 1-5 hours after the most recent administration of a bolus dose (adapted from Using Insulin© 2003).
Currently available insulin pumps generally do not use the glycemic index (GI) or glycemic indexes of the carbohydrates of the intake to determine the bolus dosage. GI is a ranking system for carbohydrates based on their effect on blood glucose levels. According to this system, glucose, the fastest-acting carbohydrate, is given a value of 100, and other carbs are ranked relative to that measurement. Ripeness, cooking time, fiber, and fat content can all impact how a food affects the blood glucose (BG). A low GI food will release glucose more slowly and steadily. A high GI food causes a more rapid rise in blood glucose levels. The table in FIG. 4 lists different types of foods and their respective GI's.